Organic electroluminescent device, display, and illuminating device

ABSTRACT

An organic electroluminescent element including at least an emission layer sandwiched between an anode and a cathode, wherein the emission layer comprises at least a compound represented by Formula (A),

TECHNICAL FIELD

The present invention relates to an organic electroluminescent element,a display device and a lighting device.

BACKGROUND

Conventionally, an emission type electronic display device includes anelectroluminescence display (hereinafter, referred to as an ELD). Aconstituent element of ELD includes such as an inorganicelectroluminescent element and an organic electroluminescent element(hereinafter, referred to as an organic EL element). An inorganicelectroluminescent element has been utilized as a flat light source,however, requires a high voltage of alternating current to operate anemission element.

An organic electroluminescent element is an element provided with aconstitution comprising an emission layer containing a emittingsubstance being sandwiched with a cathode and an anode, and an excitonis generated by an electron and a positive hole being injected into theemission layer to be recombined, resulting emission utilizing lightrelease (fluorescence-phosphorescence) at the time of deactivation ofsaid exciton; the emission is possible at a voltage of approximately afew to a few tens volts, and an organic electroluminescent element isattracting attention with respect to such as superior viewing angle andhigh visual recognition due to a self-emission type as well as spacesaving and portability due to a completely solid element of a thin layertype.

However, in an organic electroluminescence in view of the futurepractical application, desired has been development of an organic ELelement which efficiently emits at a high luminance with a low electricconsumption.

In Japanese Patent No. 3093796, a slight amount of a fluorescentsubstance has been doped in a stilbene derivative, distyrylarylenederivative or a tristyrylarylene derivative, to achieve improvedemission luminance and a prolonged lifetime of an element.

Further, there are known such as an element having an organic emissionlayer comprising a 8-hydroxyquinoline aluminum complex as a hostcompound which is doped with a slight amount of a fluorescent substance(for example, JP-A 63-264692 (hereinafter, JP-A refers to JapanesePatent Publication Open to Public Inspection No.)) and an element havingan organic emission layer comprising a 8-hydroxyquinoline aluminumcomplex as a host compound which is doped with quinacridone type dye(for example, JP-A 3-255190).

In the case of utilizing emission from an excited singlet as describedabove, since a generation ratio of a singlet exciton to a tripletexciton is 1:3, that is, a generation probability of an emitting excitonspecies is 25% and a light taking out efficiency is approximately 20%,the limit of a quantum efficiency (ηext) of taking out is said to be 5%.

However, since an organic EL element which utilizes phosphorescence froman excited triplet has been reported from Princeton University (M. A.Baldo et al., Nature vol. 395, pp. 151-154 (1998)), researches onmaterials exhibiting phosphorescence at room temperature have come to beactive.

For example, it is also disclosed in A. Baldo et al., Nature, vol. 403,No. 17, pp. 750-753 (2000), and U.S. Pat. No. 6,097,147.

Since the upper limit of internal quantum efficiency becomes 100% byutilization of an excited triplet, which is principally 4 times of thecase of an excited singlet, it may be possible to achieve almost thesame ability as a cooled cathode ray tube to attract attention also foran illumination application.

For example, in such as S. Lamansky et al., J. Am. Chem. Soc., vol. 123,p. 4304 (2001), many compounds mainly belonging to heavy metal complexessuch as iridium complexes have been synthesized and studied.

Further, in aforesaid, A. Baldo et al., Nature, vol. 403, No. 17, pp.750-753 (2000), utilization of tris(2-phenylpyridine)iridium as a dopanthas been studied.

In addition to these, M. E. Tompson et al., at The 10th InternationalWorkshops on Inorganic and Organic Electroluminescence (EL'00,Hamamatsu), have studied to utilize L₂Ir(acac) such as (ppy)₂Ir(acac) asa dopant, Moon-Jae Youn. Og., Tetsuo Tsutsui et al., also at The 10thInternational Workshops on Inorganic and Organic Electroluminescence(EL'00, Hamamatsu), have studied utilization of such astris(2-(p-tolyl)pyridine)iridium (Ir(ptpy)₃) andtris(benzo[h]quinoline)iridium (Ir(bzq)₃) (herein, these metal complexesare generally referred to as orthometalated iridium complexes.).

Further, in also the aforesaid, S. Lamansky et al., J. Am. Chem. Soc.,vol. 123, p. 4304 (2001), studies have been carried out to prepare anelement utilizing various types of iridium complexes.

Further, to obtain high emission efficiency, Ikai et al., at The 10thInternational Workshops on Inorganic and Organic Electroluminescence(EL'00, Hamamatsu) utilized a hole transporting compound as a host of aphosphorescent compound. Further, M. E. Tompson et al. utilized varioustypes of electron transporting materials as a host of a phosphorescentcompound doped with a new iridium complex.

Further, at present, organic EL elements employing such iridiumcomplexes are mostly prepared via vapor deposition. Preparation oforganic EL elements via coating methods has increasingly beeninvestigated. However, at present, low solubility of iridium complexesmakes preparation of such elements via the coating method difficult.Consequently, it is demanded to enhance solubility of the iridiumcomplexes.

An orthometalated complex provided with platinum instead of iridium as acenter metal is also attracting attention. With respect to these typesof complexes, many examples having a characteristic ligand are known(for example, refer to Patent Documents 1-5).

In any case, emission luminance and emission efficiency aresignificantly improved compared to conventional elements because theemitting light arises from phosphorescence, however, there has been aproblem of a poor emission lifetime of the element compared toconventional elements. It is hard to achieve an emission of a shortwavelength and an improvement of an emission lifetime of the element fora phosphorescent emission material provided with a high efficiency. Atpresent state, it cannot be achieved a level of a practical use.

As those which improve the above, known are Ir complexes and Ptcomplexes which employ phenylimidazole derivatives as a ligand (refer,for example, to Patent Documents 6 and 7). However, the light emissionefficiency of these complexes and the lifetime of elements areinsufficient, whereby more enhanced efficiency and lifetime of elementsare being sought.

Further disclosed as light emitting materials which excel in desiredcharacteristics are polymers having a hetero-condensation polycyclicstructure as a repeating unit (refer, for example, to Patent Document8). However, those materials are limited to polymer compounds, and nodescription is made with regard to the terminal substituent, whereby itis difficult to estimate excellent characteristics in the case in whicha specific substituent is substituted.

-   [Patent Document 1] JP-A 2002-332291-   [Patent Document 2] JP-A 2002-332292-   [Patent Document 3] JP-A 2002-338588-   [Patent Document 4] JP-A 2002-226495-   [Patent Document 5] JP-A 2002-234894-   [Patent Document 6] WO 02/15645-   [Patent Document 7] WO 05/7767-   [Patent Document 8] WO 05/26231

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of this invention is to provide an organic electroluminescentelement having high emission efficiency and long emission lifetime, adisplay device and a lighting device comprising the organicelectroluminescent element.

Means to Solve the Problems

An object of the present invention described above has been achieved bythe following constitutions.

1. An organic electroluminescent element comprising at least an emissionlayer sandwiched between an anode and a cathode,

wherein the emission layer comprises at least a compound represented byFormula (A),

wherein X and Y each represent O, S or N—R(R represents a hydrogen atomor a substituent); A¹ and A² each represent a hydrogen atom or asubstituent and at least one of A¹ and A² is a substituent; L¹ and L²each represent a divalent linking group; n is an integer of 1 or more;n1 and n2 each are an integer of 0 or more; n3 and n4 each are 0 or 1;provided that n1+n2≧2.

2. The organic electroluminescent element of item 1, wherein thecompound represented by Formula (A) is further represented by Formula(1),

wherein X represents of O, S or N—R (R represents a hydrogen atom or asubstituent); n is an integer of 2 or more; A¹ and A² each represent ahydrogen atom or a substituent; and at least one of A¹ and A² each are asubstituent.

3. The organic electroluminescent element of item 2, wherein n is aninteger of 2 to 10.4. The organic electroluminescent element of item 2, wherein n is aninteger of 2 to 4.5. The organic electroluminescent element of item 1, wherein thecompound represented by Formula (A) is further represented by Formula(2),

wherein X and Y each represent O, S or N—R(R represents a hydrogen atomor a substituent); n1, n2 and n represent an integer of 1 or more; A¹and A² each represent a hydrogen atom or a substituent; and at least oneof A¹ and A² is a substituent.

6. The organic electroluminescent element of item 5, wherein n is aninteger of 1 to 5.7. The organic electroluminescent element of item 5, wherein n is aninteger of 1 or 2.8. The organic electroluminescent element of item 1, wherein thecompound represented by Formula (A) is further represented by Formula(3),

wherein X represents O, S or N—R(R represents a hydrogen atom or asubstituent); n is an integer of 2 or more; L¹ and L² each represent adivalent linking group; A¹ and A² each represent a hydrogen atom or asubstituent; and at least one of A¹ and A² is a substituent.

9. The organic electroluminescent element of item 8, wherein n is aninteger of 2 or more to 10.10. The organic electroluminescent element of item 8, wherein n is aninteger of 2 to 4.11. The organic electroluminescent element of any one of items 1 to 10,wherein at least one of A¹ and A² incorporate a substituent having anitrogen atom.12. The organic electroluminescent element of items 11, wherein thesubstituent having a nitrogen atom is a carbazolyl group.13. The organic electroluminescent element of items 11, wherein thesubstituent having a nitrogen atom is a carbolinyl group.14. The organic electroluminescent element of items 11, wherein thesubstituent having a nitrogen atom is a diarylamino group.15. The organic electroluminescent element of any one of items 1 to 14,wherein X is an oxygen atom.16. The organic electroluminescent element of any one of items 1 to 15,wherein the emission layer incorporates a phosphorescence-emitting metalcomplex.17. The organic electroluminescent element of items 16, wherein thephosphorescence-emitting metal complex is an Ir complex.18. The organic electroluminescent element of any one of items 1 to 17,generating emission of white color.19. A display, comprising the organic electroluminescent elementdescribed in any one of items 1 to 18.20. A lighting device comprising the organic electroluminescent elementdescribed in any one of items 1 to 18.

Effects of the Invention

According to the present invention, it has become possible to provide anorganic electroluminescent element, a display device and a lightingdevice comprising the organic electroluminescent element which resultsin high light emission efficiency and exhibits a long light emissionlife.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic constitutional view of an organic EL full-colordisplay device.

DESCRIPTION OF THE ALPHANUMERIC DESIGNATIONS

-   101 glass substrate-   102 ITO transparent electrode-   103 partition wall-   104 positive hole injecting layer-   105B, 105G, and 105R light emitting layers

BEST MODES TO CARRY OUT THE INVENTION

The organic EL element of the present invention is characterized in thata light emitting layer, which is sandwiched between an anode and acathode, incorporates at least one of the compounds represented by aboveFormula (A), and more specifically, of the compounds represented byFormulas (1)-(3).

In above Formulas (A), and (1)-(3), examples of the substituentsrepresented by A¹ and A² include an alkyl group (for example, a methylgroup, an ethyl group, a propyl group, an isopropyl group, a tert-butylgroup, a pentyl group, a hexyl group, an octyl group, a dodecyl group, atridecyl group, a tetradecyl group, and a pentadecyl group); ancycloalkyl group (for example, a cyclopentyl group and a cyclohexylgroup); an alkenyl group (for example, a vinyl group and a allyl group);an alkynyl group (for example, an ethynyl group and a propargyl group);an aryl group (for example, a phenyl group, a p-chlorophenyl group, amesityl group, a tolyl group, a xylyl group, a naphthyl group, ananthoryl group, an azulenyl group, an acenaphthenyl group, a fluorenylgroup, a phenanthryl group, an indenyl group, a pyrenyl group, and abiphenyl group); an aromatic heterocyclyl group (for example, a furylgroup, a thienyl group, a pyridyl group, a pyridazyl group, a pyrimidylgroup, a pyrazyl group, a triazyl group, an imidazolyl group, apyrazolyl group, a thiazolyl group, a benzimidazolyl group, abenzoxazolyl group, a quinazolyl group, and a phthalazyl group), aheterocyclyl group (for example, a pyrrolidyl group, an imidazolydylgroup, a morpholyl group, and an oxazolydyl group); an alkoxy group (forexample, a methoxy group, an ethoxy group, a propyloxy group, apentyloxy group, a hexyloxy group, an octyloxy group, and a dodecyloxygroup); a cycloalkoxy group (for example, a cyclopentyloxy group and acyclohexyloxy group), an aryloxy group (for example, a phenoxy group anda naphthyloxy group), an alkylthio group (for example, a methylthiogroup, an ethylthio group, a propylthio group, a pentylthio group, ahexylthio group, an octylthio group, and a dodecylthio group); acycloalkylthio group (for example, a cyclopentylthio group and acyclohexylthio group), an arylthio group (for example, a phenylthiogroup and a naphthylthio group); an alkoxycarbonyl group (for example, amethyloxycarbonyl group, an ethyloxycarbonyl group, a butyloxycarbonylgroup, an octyloxycarbonyl group, and a dodecyloxycarbonyl group); anaryloxycarbonyl group (for example, a phenyloxycarbonyl group and anaphthyloxycarbonyl group), a sulfamoyl group (for example, anaminosulfonyl group, a methylaminosulfonyl group, adimethylaminosulfonyl group, a butylaminosulfonyl group, ahexylaminosulfonyl group, a cyclohexylaminosulfonyl group, anoctylaminosulfonyl group, a dodecylaminosulfonyl group, aphenylaminosulfonyl group, a naphthylaminosulfonyl group, and a2-pyridylaminosulfonyl group); an acyl group (for example, an acetylgroup, an ethylcarbonyl group, a propylcarbonyl group, a pentylcarbonylgroup, a cyclohexylcarbonyl group, an octylcarbonyl group, a2-ethylhexylcarbonyl group, a dodecylcarbonyl group, a phenylcarbonylgroup, a naphthylcarbonyl group, and a pyridylcarbonyl group); anacyloxy group (for example, an acetyloxy group, an ethylcarbonyloxygroup, a butylcarbonyloxy group, an octylcarbonyloxy group, adodecylcarbonyloxy group, and a phenylcarbonyloxy group), an amido group(for example, a methylcarbonylamino group, an ethylcarbonylamino group,a dimethylcarbonylamino group, a propylcarbonylamino group, apentylcarbonylamino group, a cyclohexylcarbonylamino group, a2-ethylhexylcarbonylamino group, an octylcarbonylamino group, adodecylcarbonylamino group, a phenylcarbonylamino group, and anaphthylcarbonylamino group); a carbamoyl group (for example, anaminocarbonyl group, a methylaminocarbonyl group, adimethylaminocarbonyl group, a propylaminocarbonyl group, apentylaminocarbonyl group, a cyclohexylaminocarbonyl group, anoctylaminocarbonyl group, a 2-ethylhexylaminocarbonyl group, adodecylaminocarbonyl group, a phenylaminocarbonyl group, anaphthylaminocarbonyl group, and a 2-puridylaminocarbonyl group); aureido group (for example, a methylureido group, an ethylureido group, apentylureido group, a cyclohexylureido group, an octylureido group, adodecylureido group, a phenylureido group, a naphthylureido group, and a2-pyridylaminoureido group); a sulfinyl group (for example, amethylsulfinyl group, an ethylsulfinyl group, a butylsulfonyl group, acyclohexylsulfinyl group, a 2-ethylhexylsulfinyl group, adodecylsulfinyl group, a phenylsulfonyl group, a naphthylsulfinyl group,and a 2-pyridylsulfinyl group); an alkylsulfonyl group (for example, amethylsulfonyl group and an ethylsulfonyl group, a butylsulfonyl group,a cyclohexylsulfonyl group, a 2-ethylhexylsulfonyl group, and a dodecylsulfonyl group); an arylsulfonyl group (for example, a phenylsulfonylgroup, a naphthylsulfonyl group, and a 2-pyridylsulfonyl group); anamino group (for example, an amino group, an ethylamino group, adimethylamino group, a butylamino group, a cyclopentylamino group, a2-ethylhexylamino group, a dodecylamino group, an anilino group, anaphthylamine group, and a 2-pyridylamino group); a halogen atom (forexample, a fluorine atom, a chlorine atom, and a bromine atom); afluorinated hydrocarbon group (for example, a fluoromethyl group, atrifluoromethyl group, a pentafluoroethyl group, and a pentafluorophenylgroup); a cyano group; and a silyl group (for example, a trimethylsilylgroup, a triisopropylsilyl group, a triphenylsilyl group, and aphenyldiethylsilyl group). These groups may further have a substituent.

At least one of A¹ or A² is preferably a substituent incorporating anitrogen atom. Further, preferred as the substituent incorporating anitrogen atom are a carbazolyl group, a carbolinyl group, and adiarylamino group.

“Aryl of the diarylamino group”, as described herein, is as defined forthe aryl group described in the substituent represented by each of A¹and A² in Formula (A).

In Formulas (A) and (1)-(3), X and Y each represents any of O, S, andN—R (wherein R represents a substituent). The substituents representedby above R include a substituted or unsubstituted alkyl group, arylgroup, or aromatic heterocyclyl group. Specific examples thereof arethose listed in description for A¹ and A².

In Formulas (1) and (3), n is preferably 2-10, but is more preferably2-4.

In Formula (2), n3 is preferably 1-5, but is more preferably 1 or 2.

The divalent linking groups represented by each of L¹ and L² in Formulas(A) and (3) may include an alkylene group (for example, an ethylenegroup, a trimethylene group, a tetramethylene group, a propylene group,an ethylethylene group, a pentamethylene group, and a hexamethylenegroup); an alkenylene group (for example, a vinylene group, apropenylene group, a butenylene group, a pentenylene group, a1-methylvinylene group, a 1-methylpropenylene group, a2-methylpropenylene group, a 1-methylpentenylene group, a3-methylpentenylene group, a 1-ethylvinylene group, a 1-ethylpropenylenegroup, a 1-ethylbutenylene group, and a 3-ethylbutenylene group); analkynylene group (for example, an ethynylene group, a propynylene group,a 1-butynylene group, a 1-pentynylene group, a 1-hexynylene group, a2-butynylene group, a 2-pentynylene group, a 1-methylethynylene group, a3-methyl-1-propynylene group, and a 3-methyl-1-butynylene group); anarylene group (for example, an o-phenylene group, an m-phenylene group,a p-phenylene group, a naphthalenediyl group, an anthracenediyl group, anaphthacenediyl group, a pyrenediyl group, a naphthylnaphthalenediylgroup, a biphenyldiyl group (for example, a [1,1′-biphenyl]-4,4′-diylgroup, a 3,3′-biphenyldiyl group, and a 3,6-biphenyldiyl group); aterphenyldiyl group, a quaterphenyldiyl group, a kinkphenyldiyl group, asequsiphenyldiyl group, a septiphenyldiyl group, an octiphenyldiylgroup, a noviphenyldiyl group, and a deciphenyldiyl group); aheteroarylene group (for example, a carbazole ring, a carboline ring, adiazacarbazole ring (which is also called a monoazacarboline ring, andrefers to a ring structure in which one of carbon atoms whichconstitutes a carboline ring is replaced with a nitrogen atom), adivalent group derived from the group consisting of a triazole ring, apyrrole ring, a pyrazine ring, a quinoxaline ring, a thiophene ring, anoxadiazole ring, a dibenzofuran ring, a benzothiophene ring, and anindole); a divalent heterocyclyl group (for example, a divalent groupderived from a pyrrolidine ring, an imidazoline ring, a morpholine ring,and an oxazolidine ring); and a chalcogen atom such as oxygen or sulfur.

Further, applicable may be groups such as an alkylimino group, adialkylsilanediyl group, or a diarylgermanediyl group which are linkedvia a heteroatom.

Further, as above L3, preferred are an arylene group, a heteroarylenegroup, a divalent heterocyclyl group, and an alkylene group, morepreferred is the arylene group, but particularly preferred is them-phenylene group.

The specific examples represented by Formulas (A) and (1)-(3) are listedbelow, however the present invention is not limited thereto.

Constituent layers of an organic EL element of this invention will nowbe explained. Specific examples of a preferable layer constitution of anorganic EL element of this invention are shown below; however, thisinvention is not limited thereto.

(i) anode/emission layer/electron transport layer/cathode,(ii) anode/positive hole transport layer/emission layer/electrontransport layer/cathode,(iii) anode/positive hole transport layer/emission layer/positive holeinhibition layer/electron transport layer/cathode,(iv) anode/positive hole transport layer/emission layer/positive holeinhibition layer/electron transport layer/cathode buffer layer/cathode,(v) anode/anode buffer layer/positive hole transport layer/emissionlayer/positive hole inhibition layer/electron transport layer/cathodebuffer layer/cathode,

It is preferable that the organic EL element of the present inventionincorporates monochromatic light emitting layers, namely a blue lightemitting layer which emits light at a maximum wavelength in the range ofpreferably 430-480 nm, a green light emitting layer which emits lighthaving a maximum wavelength in the range of preferably 510-550 nm, and ared light emitting layer which emits light having a maximum wavelengthin the range of preferably 600-640 nm, and display devices are preparedemploying the above. Further, these three layers may be laminated toprepare a white light emitting layer. Further, a non-light emittinginterlayer may be incorporated between the light emitting layers. It ispreferable that the organic EL element of the present invention iscomposed of a white light emitting layer and that illuminating devicesare composed of the same.

Each layer which constitutes the organic EL element of the presentinvention will now be described.

<Anode>

As an anode according to an organic EL element of this invention, thosecomprising metal, alloy, a conductive compound, which is provided with alarge work function (not less than 4 eV), and a mixture thereof as anelectrode substance are preferably utilized. Specific examples of suchan electrode substance include a conductive transparent material such asmetal like Au, CuI, indium tin oxide (ITO), SnO₂ and ZnO. Further, amaterial such as IDIXO (In₂O₃—ZnO) which can prepare an amorphous andtransparent electrode, may be also utilized. As for an anode, theseelectrode substances may be made into a thin layer by a method such asevaporation or spattering and a pattern of a desired form may be formedby means of photolithography, or in the case of requirement of patternprecision is not so severe (not less than 100 μm), a pattern may beformed through a mask of a desired form at the time of evaporation orspattering of the above-described substance. Further in the case ofusing a coatable material such as an organic conductive compound, a wetfilm-forming method such as printing and coating may be utilized. Whenemission is taken out of this anode, the transmittance is preferably setto not less than 10% and the sheet resistance as an anode is preferablynot more than a few hundreds Ω/□. Further, although the layer thicknessdepends on a material, it is generally selected in a range of 10-1,000nm and preferably of 10-200 nm.

<Cathode>

On the other hand, as a cathode according to this invention, metal(referred to as an electron injection metal), alloy, a conductivecompound and a mixture thereof, which have a small work function (notmore than 4 eV), are utilized as an electrode substance. Specificexamples of such an electrode substance includes such as sodium,sodium-potassium alloy, magnesium, lithium, a magnesium/copper mixture,a magnesium/silver mixture, a magnesium/aluminum mixture, amagnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixture,indium, a lithium/aluminum mixture and rare earth metal. Among them,with respect to an electron injection property and durability againstsuch as electron injecting and oxidation, preferable are a mixture ofelectron injecting metal with the second metal which is stable metalhaving a work function larger than electron injecting metal, such as amagnesium/silver mixture, a magnesium/aluminum mixture, amagnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixture anda lithium/aluminum mixture, and aluminum.

As for a cathode, these electrode substances may be made into a thinlayer by a method such as evaporation or spattering. Further, the sheetresistance as a cathode is preferably not more than a few hundreds Ω/□and the layer thickness is generally selected in a range of 10 nm-5 μmand preferably of 50-200 nm.

Herein, to transmit emission, either one of an anode or a cathode of anorganic EL element is preferably transparent or translucent to improvethe mission luminance.

Further, after preparing the above 1-20 nm thick metal film on thecathode, electrically conductive transparent materials listed in thedescription of the anode are applied thereon, whereby it is possible toprepare a transparent or translucent cathode. By employing this, it ispossible to prepare an element in which both the anode and cathodeexhibit transmitting properties.

An injection layer, an inhibition layer, and an electron transportinglayer, which are employed as a constituting layer of the organic ELelement of the present invention, will now be described.

<Injection Layer: Electron Injection Layer, Positive Hole InjectionLayer>

An injection layer is appropriately provided and includes an electroninjection layer and a positive hole injection layer, which may bearranged between an anode and an emission layer or a positive transferlayer, and between a cathode and an emission layer or an electrontransfer layer, as described above.

An injection layer is a layer which is arranged between an electrode andan organic layer to decrease an operating voltage and to improve anemission luminance, which is detailed in volume 2, chapter 2 (pp.123-166) of “Organic EL Elements and Industrialization Front thereof(Nov. 30, 1998, published by N. T. S Corp.)”, and includes a positivehole injection layer (an anode buffer layer) and an electron injectionlayer (a cathode buffer layer).

An anode buffer layer (a positive hole injection layer) is also detailedin such as JP-A 9-45479, 9-260062 and 8-288069, and specific examplesinclude such as a phthalocyanine buffer layer comprising such as copperphthalocyanine, an oxide buffer layer comprising such as vanadium oxide,an amorphous carbon buffer layer, and a polymer buffer layer employingconductive polymer such as polythiophene.

A cathode buffer layer (an electron injection layer) is also detailed insuch as JP-A 6-325871, 9-17574 and 10-74586, and specific examplesinclude a metal buffer layer comprising such as strontium and aluminum,an alkali metal compound buffer layer comprising such as lithiumfluoride, an alkali earth metal compound buffer layer comprising such asmagnesium fluoride, and an oxide buffer layer comprising such asaluminum oxide. The above-described buffer layer (injection layer) ispreferably a very thin layer, and the layer thickness is preferably in arange of 0.1 nm-5 μm although it depends on a raw material.

<Inhibition Layer; Positive Hole Inhibition Layer, Electron InhibitionLayer>

Inhibition layer can be appropriately utilized in addition to basicconstitution layers of a thin film comprising organic compounds asstated above.

For example, a positive inhibition layer described in such as JP-A Nos.11-204258 and 11-204359 and p. 237 of “Organic EL Elements andIndustrialization Front Thereof (Nov. 30 (1998), published by N. T. SCorp.)” is applicable to a positive hole inhibition (hole block) layer.

A positive hole inhibition layer, in a broad meaning, is provided with afunction of electron transport layer, being comprised of a materialhaving a function of transporting an electron but a very small abilityof transporting a positive hole, and can improve the recombinationprobability of an electron and a positive hole by inhibiting a positivehole while transporting an electron. Further, a constitution of anelectron transport layer described later can be appropriately utilizedas a positive hole inhibition layer according to this invention.

It is preferable that the positive hole inhibition layer of the organicEL element of the present invention is arranged adjacent to the lightemitting layer. It is preferable that the positive hole inhibition layerincorporates the compounds represented by above Formula (A) and (1)-(3).

Further, in the present invention, in the presence of a plurality oflight emitting layers which emit a plurality of different colors oflight, it is preferable that the light emitting layer which emits themaximum amount of light of the shortest wavelength of all the lightemitting layers, is nearest the anode. In such a case, it is preferablethat a positive hole inhibition layer is additionally arranged betweenthe above shortest wavelength light emitting layer and the lightemitting layer which is nearest the anode, except for the above layer.Further, it is preferable that an ionization potential of at least 50%by weight of the compounds, incorporated in the positive hole inhibitionlayer arranged in the above position, is 0.3 eV higher than that of thehost compounds of the above shortest wavelength light emitting layer.

Ionization potential is defined as energy required to transfer anelectron in the highest occupied molecular orbital to the vacuum level,and is determined by the methods described below:

(1) it is possible to determine ionization potential in such a mannerthat the value, which is calculated by performing structuraloptimization by employing Gaussian 98 (Gaussian 98, Revision A. 11.4, MJ. Frisch, et al., Gaussian, Inc., Pittsburgh Pa., 2002) andB3LYP/6-31G* as a key word, and the calculated value (being the value interms of eV unit) is rounded off at the second decimal place. Backgroundin which the above calculated value is effective is that the calculatedvalues obtained by the above method and experimental values exhibit highcorrelation.(2) it is also possible to obtain ionization potential via a directmeasurement method employing a photoelectron spectroscopy. For example,it is possible to appropriately employ a low energy electronspectrometer “Model AC-1”, produced by Riken Keiki Co., Ltd., or amethod known as ultraviolet photoelectron spectroscopy.

On the other hand, an electron inhibition layer is, in a broad meaning,provided with a function of a positive hole transport layer, beingcomprised of a material having a function of transporting a positivehole but a very small ability of transporting an electron, and canimprove the recombination probability of an electron and a positive holeby inhibiting an electron while transporting a positive hole. Further, aconstitution of a positive hole transport layer described later can beappropriately utilized as an electron inhibition layer. The layerthickness of a positive hole inhibition layer and an electron transportlayer of the present invention is preferably in a range of 3-100 nm,more preferably in a range of 5-30 nm.

Light Emitting Layer

The light emitting layer according to the present invention results inlight emission via recombination of electrons and positive holesinjected from the electrode or the electron transporting layer, and thepositive hole transporting layer, and the light emitting portion may bein the interior of the light emitting layer or at the interface betweenthe light emitting layer and the adjacent layer thereto.

The light emitting layer of the organic EL element of the presentinvention incorporates, as a host compound, the compounds represented byabove Formula (A) and (1)-(3). In the present invention, simultaneouslyemployed may be conventional host compounds.

In the present invention, a host compound is defined as a compoundfeaturing a mass ratio of at least 20% in an emission layer based on allthe compounds incorporated therein and exhibiting a phosphorescencequantum efficiency of less than 0.1 in terms of phosphorescence emissionat room temperature (25° C.). The phosphorescence quantum efficiency ispreferably less than 0.01.

Further, as the host compound, a plurality of conventional host compoundmay be used in combination. Using a plurality of host compounds at thesame time makes it possible to adjust charge transfer and to enhanceefficiency of an organic EL element. Still further, using a compoundrepresented by the Formulas (A), (1)-(3), makes it possible to mixdifferent emission light components, resulting in any given emissioncolor. Emission of white color can be obtained by adjusting species ofemitting metal complexes and dope amount and it is further usefullyapplied for a light sources or a backlight.

A specific emission host in combination use is preferably a compoundhaving a positive hole transporting ability and an electron transportingability, as well as preventing elongation of an emission wavelength andhaving a high Tg (a glass transition temperature).

As specific examples of an emission host compounds described in thefollowing Documents are preferable:

For example, JP-A Nos. 2001-257076, 2002-308855, 2001-313179,2002-319491, 2001-357977, 2002-334786, 2002-8860, 2002-334787,2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75645,2002-338579, 2002-105445, 2002-343568, 2002-141173, 2002-352957,2002-203683, 2002-363227, 2002-231453, 2003-3165, 2002-234888,2003-27048, 2002-255934, 2002-260861, 2002-280183, 2002-299060,2002-302516, 2002-305083, 2002-305084 and 2002-308837.

In the present invention, when a plurality of light emitting layers isincorporated, it is preferable that in view of ease of obtaining auniform film state over the entire organic layer, at least 50% by weightof the host compounds in each layer are of the same compound. Further,it is preferable that the phosphorescence emitting energy of the abovecompound is at least 2.9 eV so that it becomes more advantageous toefficiently retard the energy transfer from the dopant to result inhigher luminance.

“Phosphorescence emitting energy”, as described in the present inventionrefers to the peak energy of the 0-0 transition band of phosphorescenceemission which is obtained by determining photoluminescence of a 100 nmvapor deposition film of the host compound on a substrate.

It is preferable that the phosphorescence emitting energy and Tg of hostcompounds employed in the present invention are at least 2.9 eV and atleast 90° C., respectively. When the Tg is at most 90° C., deterioration(a decrease in luminance and degradation of film state) of the elementduring storage is marked, resulting in not meeting market needs as alight source. Namely, in order to satisfy both luminance and durability,those which exhibit the phosphorescence emitting energy of at least 2.9eV and a Tg of at least 90° C. are preferred. Tg is more preferably atleast 100° C.

In the present invention, when a plurality of light emitting layers isincorporated, it is preferable that at least 50% by weight of the hostcompounds in the light emitting layer are the same compound whichexhibits a phosphorescence emitting energy of at least 2.9 eV and Tg ofat least 90° C. Surprisingly, it was discovered that even though eachmaterial which exhibits excellent durability is employed, when adifferent compound is employed in each layer, storage characteristics ofthe entire element are occasionally degraded compared to the case inwhich the same compound is employed in all light emitting layers.

This cause is not yet fully understood, however, the cause is assumed tobe as follows. When 50% by weight of host compounds in all lightemitting layers are the same, namely, when the host compounds of alllight emitting layers are substantially the same, a uniform film surfacestate tends to be obtained. When different compounds are employed ineach light emitting layer, even though each compound is stable,non-uniformity tends to occur at the layer interface.

Phosphorescence emitting metal complexes are compounds which results inobserved of light emission from the excited triplet, emitphosphorescence at room temperature (25° C.), and exhibit aphosphorescent quantum yield of at least 0.01 at 25° C.

The phosphorescent quantum yield is preferably at least 0.1. It possibleto determine the above phosphorescent quantum yield via the methoddescribed on page 398 of Bunko (Spectroscopy) II of Dai 4 Han JikkenKagaku Koza (4th Edition Experimental Chemistry Lectures) 7 (1992Edition, Maruzen).

It is possible to determine the phosphorescent quantum yield in asolution by employing various solvents. The phosphorescence emittingmetal complexes may be employed in the present invention as long as theyresult in the above phosphorescent quantum yield in any of the solvents.

The light emitting principle of phosphorescence emitting metal complexesis of two types: one is an energy transfer type in which carriersundergo recombination on the host compounds to which carriers aretransported to generate an excited state of the host compounds and bytransferring the resulting energy to phosphorescence emitting complexes,light emission is obtained, and the other is a carrier trap type inwhich phosphorescence emitting metal complexes work as a carrier trapand carriers undergo recombination on the phosphorescence emitting metalcomplexes, whereby it is possible to obtain light emission from thephosphorescence emitting metal complexes. In either case, an essentialcondition is that energy of the excited state of phosphorescenceemitting metal complexes is lower than that of the excited state of hostcompounds.

Phosphorescence emitting metal complexes according to the presentinvention are exemplified below. Those which are preferably employed arecomplexes and those which are more preferably employed are Ir complexeswhich have 2-phenylimidazole derivatives as a ligand.

It is possible to synthesize these compounds with reference to themethods described, for example, in Inorg. Chem. Volume 40, 1704-1711.

In the present invention, the maximum wavelength of phosphorescenceemitted by phosphorescence emitting organic metal complexes is notparticularly limited. In principle, it is possible to change thewavelength of emitted light by appropriately selecting the centralmetal, the ligand, and the substituent of the ligand.

Color of light emitted from the organic EL elements of the presentinvention and the compounds according to the present invention isspecified in such a manner that results determined by spectroradiometricluminance meter CS-1000 (produced by Konica Minolta Sensing Inc.) areapplied to the CIE chromaticity coordinates in FIGS. 4 and 16 on page108 of “Shinpen Shikisai Kagaku Handbook (New Edition Color ScienceHandbook”) (edited by The Color Science Association of Japan, Universityof Tokyo Press, 1955).

“White element”, as described in the present invention, means that whenfront luminance of a viewing angle of 2° C. is determined via the abovemethod, chromaticity in the CIE 1931 Chromaticity System at 1,000 Cd/m²is in the range of X=0.33±0.07 and Y=0.33±0.07.

It is possible to form the light emitting layer in such a manner thatthe above compounds are modified to a film employing the conventionalthin film producing methods such as a vacuum deposition method, a spincoating method, a casting method, an LB method, or an ink-jet method.

In the present invention, the light emitting layer incorporates layerswhich differ in spectra of the emitted light so that the wavelength ofeach maximum emitted light is in the range of 430-480 nm, 510-550 nm and600-640 nm, or a layer composed of the those laminated layers.

Laminated layer order in the light emitting layer is not particularlylimited, and a non-light emitting interlayer may be provided between thelight emitting layers. In the present invention, it is preferable thatof all light emitting layers, at least one blue light emitting layer isprovided in the position which is nearest to the anode.

Further, when at least four light emitting layers are arranged, in orderto enhance luminance stability, it is preferable to laminate layers inthe anode-near order of blue, green, and red, such asblue/green/red/blue, blue/green/red/blue/green, orblue/green/red/blue/green/red.

The total thickness of light emitting layers is not particularlylimited. In view of enhancement of homogeneity of the film andenhancement of stability of emitted light color against driving electriccurrent while emitting light at low voltage, the above thickness isselected to be preferably in the range of 2 nm-5 μm, but to be morepreferably in the range of 2-200 nm. In the present invention, thethickness is most preferably in the range of 10-20 nm.

Thickness of each light emitting layer is selected to be preferably inthe range of 2-100 nm, but to be more preferably in the range of 2-20nm. The relationship of thickness of each of the blue, green, and redlight emitting layer is not particularly limited. However, it ispreferable that of the three light emitting layers, the blue lightemitting layer is thickest (in the case of presence of a plurality ofblue layers, the total thickness).

Further, a plurality of light emitting compounds may be blended in eachlight emitting layer in a range in which the above emission maximumwavelength is maintained. For example, blended in the blue lightemitting layer may be blue light emitting compounds exhibiting a maximumemission wavelength of 430-480 nm and green light emitting compoundsexhibiting a maximum emission wavelength of 510-550 nm.

<Positive Hole Transport Layer>

A positive hole transport layer contains a material having a function oftransporting a positive hole, and in a broad meaning, a positive holeinjection layer and an electron inhibition layer are also included in apositive hole transport layer. A single layer of or plural layers of apositive hole transport layer may be provided.

A positive hole transport material is those having any one of a propertyto inject or transport a positive hole or a barrier property to anelectron, and may be either an organic substance or an inorganicsubstance. For example, listed are a triazole derivative, an oxadiazolederivative, an imidazole derivative, a polyarylalkane derivative, apyrazolone derivative, a phenylenediamine derivative, a arylaminederivative, an amino substituted chalcone derivative, an oxazolederivatives, a styrylanthracene derivative, a fluorenone derivative, ahydrazone derivative, a stilbene derivative, a silazane derivative, ananiline type copolymer, or conductive polymer oligomer and specificallypreferably such as thiophene oligomer.

As a positive hole transport material, those described above can beutilized, however, it is preferable to utilized a porphyrin compound, anaromatic tertiary amine compound and a styrylamine compound, andspecifically preferably an aromatic tertiary amine compound.

Typical examples of an aromatic tertiary amine compound and astyrylamine compound include N,N,N′,N′-tetraphenyl-4,4′-diaminophenyl;N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TPD); 2,2-bis(4-di-p-tolylaminophenyl)propane;1,1-bis(4-di-p-tolylaminophenyl)cyclohexane; N,N,N′,N′-tetra-p-tolyl4,4′-diaminobiphenyl;1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;bis(4-dimethylamino-2-methylphenyl)phenylmethane;bis(4-di-p-tolylaminophenyl)phenylmethane;N,N′-diphenyl-N,N′-di(4-methoxyphenyl)-4,4′-diaminobiphenyl;N,N,N′,N′-tetraphenyl-4,4′-diaminophenylether;4,4′-bis(diphenylamino)quarterphenyl; N,N,N-trip-tolyl)amine;4-(di-p-tolylamino)-4′-[4-(di-p-triamino)styryl]stilbene;4-N,N-diphenylamino-(2-diphenylvinyl)benzene; 3-methoxy-4′-N,N-diphenylaminostilbene; and N-phenylcarbazole, in addition to thosehaving two condensed aromatic rings in a molecule described in U.S. Pat.No. 5,061,569, such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(NPD), and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(MDTDATA), in which three of triphenylamine units are bonded in a starburst form, described in JP-A 4-308688.

Polymer materials, in which these materials are introduced in a polymerchain or constitute the main chain of polymer, can be also utilized.

Further, an inorganic compound such as a p type-Si and a p type-SiC canbe utilized as a positive hole injection material and a positive holetransport material.

Further, it is possible to employ so-called p-type positive holetransporting materials which are described in JP-A No. 11-251067 and J.Huang et al., report (Applied Physics Letters 80 (2002). P. 139). In thepresent invention, since it is possible to prepare a more efficientlight emitting element, it is preferable to employ these materials.

This positive hole transport layer can be prepared by forming a thinlayer made of the above-described positive hole transport materialaccording to a method well known in the art such as a vacuum evaporationmethod, a spin coating method, a cast method, an inkjet method and a LBmethod. The layer thickness of a positive hole transport layer is notspecifically limited, however, is generally 5 nm-5 μm, preferably 5-200nm. This positive transport layer may have a single layer structurecomprised of one or not less than two types of the above describedmaterials.

Further, it is possible to employ an impurity-doped positive holetransporting layer exhibiting high “p” property. As such examples,listed are those described in each of JP-A Nos. 4-297076, 2000-196140,and 2001-102175, as well as J. Appl, Phys., 95, 5773 (2004).

In the present invention, it is preferable to employ such a positivehole transporting layer exhibiting high “p” property, since it ispossible to prepare an element which results in low electrical powerconsumption.

<Electron Transport Layer>

An electron transfer layer is comprised of a material having a functionto transfer an electron, and an electron injection layer and a positivehole inhibition layer are included in an electron transfer layer in abroad meaning. A single layer or plural layers of an electron transferlayer may be provided.

In case of utilizing in a single electron transport layer and aplurality of layers, an electron transfer material in an electrontransport layer arranged adjacent to cathode (combining in a holeinhabitation material) is provided with a function to transmit anelectron injected from a cathode to an emission layer, and compoundsconventionally well known in the art can be utilized by arbitrarilyselection as a material thereof, for examples, a nitro-substitutedfluorene derivative, a diphenylquinone derivative, a thiopyradineoxidederivative, carbodiimide, a fluorenylidenemethane derivative,anthraquinonedimethane and anthrone derivatives, and an oxadiazolederivative. Further, a thiazole derivative in which an oxygen atom inthe oxadiazole ring of the above-described oxadiazole derivative issubstituted by a sulfur atom, and a quinoxaline derivative having aquinoxaline ring which is known as an electron attracting group can beutilized as an electron transfer material. Further polymer materials, inwhich these materials are introduced in a polymer chain or thesematerials form the main chain of polymer, can be also utilized.

Further, a metal complex of a 8-quinolinol derivative such astris(8-quinolinol)aluminum (Alq),tris(5,7-dichloro-8-quinolinol)aluminum, tris(5,7-dibromo-8-quinolinol)aluminum, tris(2-methyl-8-quinolinol)aluminum,tris(5-methyl-8-quinolinol)aluminum and bis(8-quinolinol)zinc (Znq); andmetal complexes in which a central metal of the aforesaid metalcomplexes is substituted by In, Mg, Cu, Ca, Sn, Ga or Pb, can be alsoutilized as an electron transfer material. Further, metal-free or metalphthalocyanine, or those the terminal of which is substituted by analkyl group and a sulfonic acid group, can be preferably utilized as anelectron transfer material. Further, distyrylpyrazine derivative, whichhas been exemplified as a material of an emission layer, can be alsoutilized as an electron transfer material, and, similarly to the case ofa positive hole injection layer and a positive hole transfer layer, aninorganic semiconductor such as an n-type-Si and an n-type-SiC can bealso utilized as an electron transfer material.

This electron transport layer can be prepared by forming a thin layermade of the above-described electron transport material according to amethod well known in the art such as a vacuum evaporation method, a spincoating method, a cast method, an inkjet method and a LB method. Thelayer thickness of an electron transport layer is not specificallylimited; however, is generally 5 nm-5 μm, and preferably 5-200 nm. Thiselectron transport layer may have a single layer structure comprised ofone or not less than two types of the above described materials.

Further, it is possible to employ an impurity-doped electrontransporting layer exhibiting high “n” property. Examples thereofinclude those described in JP-A No. 4-297076, 10-270172, 2000-196140,and 2001-102175, as well as J. Appl. Phys., 95, 5773 (2004).

In the present invention, it is preferable to employ such an electrontransporting layer exhibiting high “n” property, since it is possible toprepare an element winch results in low electrical power consumption.

<Substrate>

A substrate (also referred to as Base Plate, Base Material or Support)according to an organic EL element of the present invention is notspecifically limited with respect to types of such as glass and plasticsprovided being transparent, however, a substrate preferably utilizedincludes such as glass, quartz and transparent resin film. Aspecifically preferable substrate is resin film capable of providing anorganic EL element with a flexible property.

Resin film includes such as film comprised of a polyester such aspolyethylene terephthalate (PET) and polyethylene naphthalate (PEN);polyethylene, polypropyrene, a cellulose ester or a cellulose esterderivative such as cellophane, cellulose diacetate, cellulosetriacetate, cellulose acetate butylate, cellulose acetate propionate(CAP), cellulose acetate phtalate(TAC), cellulose nitrate; polyvinylidene chloride, polyvinyl alcohol, polyethylene vinylalcohol,syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide, polyether sulphone (PES),polyphenylene sulfide, polysulphones, polyether imide, polyether ketoneimide, poly amide, fluorine contained resin, nylon,polymethylmethacrylate, acrylates or polyacrylates, ARTON (Product byJSR Corporation), and cyclo olefin resin such as APEL(Product name byMitsui Chemicals, Inc).

On the surface of resin film, an inorganic or organic cover layer or ahybrid cover layer comprising the both may be formed, and the film ispreferably provided with a high barrier ability. A preferably barrierfilm has a moisture permeability of not more than 0.01 g/(m²·24 hr)·at atemperature of 25±0.5° C., relative humidity (90±2)% RH, measured basedon JIS K 7129-1992, and more preferably an oxygen permeability of notmore than 1×10⁻³ ml/(m²·24 hr·MPa) measured based on JIS K 7126-1987 anda moisture permeability of not more than 1×10⁻⁵ g/(m²·24 hr).

As barrier film forming materials, employed may be those which functionto retard invasion of materials, such as moisture or oxygen, whichdeteriorate the element. It is possible to employ, for example, siliconoxide, silicon dioxide and silicon nitride. Further, to improvebrittleness of the above film, it is preferable to result in a laminatedlayer structure composed of these inorganic layers and organicmaterials. The order of laminated inorganic layers and organic layers isnot particularly limited, but it is preferable that both are alternatelylaminated several times.

Forming methods of barrier films are not particularly limited, and it ispossible to employ, for example, a vacuum deposition method, asputtering method, a reactive sputtering method, a molecular beamepitaxy method, a cluster ion beam method, an ion plating method, aplasma polymerizing method, an atmospheric pressure plasma polymerizingmethod, a plasma CVD method, a laser CVD method, a thermal CVD method,and a coating method. The atmospheric pressure plasma polymerizingmethod, described in JP-A No. 2004-68143, is particularly preferred.

Examples of opaque substrates include metal plates composed of aluminumor stainless steel, films, opaque resin substrates, and ceramicsubstrates.

The exterior taking-out efficiency of light emitted by an organic ELelement is preferably at least 1%, but is more preferably at least 5%.Herein, exterior taking-out quantum yield (in %)=number of photons whichare emitted to the exterior of an organic EL element/number of electronswhich are flown to the organic EL element×100.

Further, simultaneously employed may be hue improving filters such ascolor filters or color conversion filters which modify the color oflight emitted from an organic EL element to multicolor, employingphosphors. When color conversion filters are employed, the λmax of lightemitted by the organic EL element is preferably at most 480 nm.

<<Sealing>>

An example of a sealing method employed in the present invention mayinclude a method in which a sealing member and an electrode, or asubstrate are adhered via adhesive agents.

The sealing member may be arranged to cover the display portion of anorganic EL element, and may be either a concave plate or a flat plate.Further, its transparency and electric insulation are of no particularconcern.

Specifically listed are glass plates, polymer plate-films, and metalplate-films. Glass plates may specifically include soda lime glass,barium-strontium containing glass, lead glass, aluminosilicic acidglass, boron silicic acid glass, barium silicic acid glass, and quartzglass. Further, listed as polymer plates may be those composed ofpolycarbonate, acryl, polyethylene terephthalate, polyether sulfide, andpolysulfone. Metal plates include those composed of at least oneselected from the group consisting of stainless steel, iron, copper,aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum,silicon, germanium, and tantalum.

In the present invention, in view of the capability of modifying anelement to a thin film, it is preferable to employ polymer films andmetal films. Furthermore, it is preferable that the polymer filmsexhibit an oxygen permeability of at most 1×10⁻³ ml/(m²·24 hours·MPa),determined by the method based on JIS K 7126-1987, and a moisturepermeability (at 25±0.5° C. and relative humidity of 90±2%) of 10⁻⁵g/(m²·24 hours), determined by the method based on JIS K 7129-1992.

In order to form concave modify sealing members, employed are a sandblasting process or a chemical etching process.

Specific adhesive agents may include photocurable and thermally curabletype adhesive agents having a reactive vinyl group of acrylic acidoligomers and methacrylic acid oligomers, as well as moisture curabletype adhesive agents such as 2-cyanoacrylic acid esters. Further listedmay be thermally and chemically curable types (being a two-liquidmixture) such as epoxy based ones. Further listed may be hot-melt typepolyamides, polyesters, and polyolefin. Still further listed may becationically curable type ultraviolet ray curable type epoxy resinadhesive agents.

Since organic EL elements occasionally deteriorate due to thermalprocessing, preferred are those which enable adhesion curing betweenroom temperature and 80° C. Further, desiccating agents may be dispersedinto the above adhesive agents. Adhesive agents may be applied tosealing portions employing a commercial dispenser, or may be printed inthe same manner as screen printing.

Further, it is appropriate to prepare a sealing film by forminginorganic material and organic material layers which come into contactwith a substrate in such a manner that on the exterior of an electrodewhich interposes an organic layer and faces the substrate, the aboveelectrode and an organic layer are thereby covered. In such case,materials to form the above film may be employable as long as theyretard invasion of those, such as moisture or oxygen, which result indeterioration of the elements. For example, employed may be siliconoxide, silicon dioxide, or silicon nitride. Further, in order tominimize brittleness of the above film, it is preferable to form alaminated layer structure composed of these inorganic layers and layerscomposed of organic materials. Formation methods of these films are notparticularly limited, and examples thereof may include a vacuumdeposition method, a sputtering method, a reactive sputtering method, amolecular beam epitaxy method, a cluster ion beam method, an ion platingmethod, a plasma polymerizing method, an atmospheric pressure plasmapolymerizing method, a plasma CVD method, a laser CVD method, a thermalCVD method, and a coating method.

It is preferable that in a gas or liquid phase, inert gases such asnitrogen or argon, or inert liquids such as fluorinated hydrocarbon orsilicone oil are injected into the space between the sealing member andthe display region. Further, it is possible to form vacuum. Stillfurther, it is possible to enclose hygroscopic compounds in theinterior.

Examples of hygroscopic compounds include metal oxides (for example,sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesiumoxide, and aluminum oxide); sulfates (for example, sodium sulfate,calcium sulfate, magnesium sulfate, and cobalt sulfate); metal halides(for example, calcium chloride, magnesium chloride, cesium fluoride,tantalum fluoride, cerium bromide, magnesium bromide, barium iodide, andmagnesium iodide); and perchlorates (for example, barium perchlorate andmagnesium perchlorate). Of the sulfates, metal halides, andperchlorates, anhydrous salts thereof are appropriately employed.

<<Protective Films and Protective Plates>>

In order to enhance mechanical strength of elements, a protective filmor plate may be arranged on the exterior of the above sealing film whichinterposes the organic layer and faces the substrate or the abovesealing film. Specifically, when sealing is carried out via the abovesealing film, its mechanical strength is not always sufficient.Consequently, it is preferable to arrange such a protective film orplate. Employable materials include glass plate, polymer plate-film, andmetal plate-film which are the same as those employed for the abovesealing. In view of light weight and capability of forming a thin film,it is preferable to employ a polymer film.

<<Light Taking-Out>>

It is generally stated that with regard to an organic EL element, lightis generated in the interior of the layer of a higher refractive index(a refractive index of 1.7-2.1) than that of air and of light generatedin the light emitting layer, only about 15% to about 20% of the light istaken out. The reasons are that light which is incident to the interface(the interface between the transparent substrate and air) at angle θ,which is greater than the critical angle, is not taken out of theelement due to total reflection, while all light is reflected betweenthe transparent electrode or the light emitting layer and thetransparent substrate, and light is channeled to the transparentelectrode or the light emitting layer, whereby light escapes to theelement side direction.

Examples of methods to enhance the light taking-out efficiency include:a method in which asperity is formed on the surface of a transparentsubstrate and total reflection at the interface between the transparentsubstrate and air is minimized (U.S. Pat. No. 4,774,435), a method inwhich a light collecting substrate is used (JP-A No. 63-314795), amethod in which a reflective surface is formed on the side surface of anelement (JP-A No. 1-220394), a method in which a flat layer of anintermediate refractive index is introduced between a substrate and alight emitting body, whereby an antireflective film is formed (JP-A No.62-172691), a method in which between a substrate and a light emittingbody introduced is a flat layer of a refractive index which is lowerthan that of the above substrate (JP-A No. 2001-202827), and a method inwhich diffraction gratings are formed between any of a substrate, atransparent electrode layer, and a light emitting layer (includingbetween a substrate and an exterior) (JP-A No. 11-283751).

In the present invention, it is possible to employ any of the abovemethods in combination with the organic EL element of the presentinvention, and it is possible to appropriately employ the method whichintroduces a flat layer of a refractive index which is lower than thatof the substrate between the above substrate and the light emittingbody, or the method in which diffraction gratings are formed between thesubstrate and either the transparent electrode layer or the lightemitting layer (including between the substrate and the exterior.

In the present invention, by combining these methods, it is possible toprepare an element which exhibits higher luminance or higher durability.

When a medium of a low refractive index is formed at a thickness whichis greater than the light wavelength between the transparent electrodeand the transparent substrate, taking-out efficiency of light emittedfrom the transparent electrode increases as the refractive index of themedium decreases.

Examples of layers of a low refractive index include aerogels, poroussilica, magnesium fluoride, and fluorine based polymers. Since therefractive index of the transparent substrate is commonly about1.5-about 1.7, the refractive index of low refractive index layers ispreferably at most about 1.5, but is more preferably at most 1.35.

Further, the thickness of low refractive index media is preferably atleast twice the wavelength in media. The reason for this is that thethickness of low refractive index media roughly approaches the lightwavelength so that electromagnetic wave permeated via evanescent entersthe substrate, whereby effects of the low refractive index layer aredecreased.

The method which employs an interface which results in total reflectionor introduces diffraction gratings into media exhibits features whichresult in a high effect to enhance light taking-out efficiency. Thesemethods are achieved as follows. By utilizing properties of theso-called Bragg diffraction in which diffraction gratings result inprimary diffraction and secondary diffraction so that it is possible tochange light direction to the specified direction which is differentfrom the diffraction, of light generated from the light emitting layer,light which is not able to going out due to the total reflection betweenthe layers is diffracted at the interface between any layers or byintroducing diffraction gratings into media (within the transparentsubstrate or within the transparent electrode), whereby light isintroduced into the exterior.

It is preferable that the introduced diffraction gratings exhibittwo-dimensional cyclic refractive indices. The reason is that since thelight emitting layer randomly emits light in all directions, a commonone-dimensional diffraction grating, which carries a cyclic refractiveindex distribution only in a certain direction, diffracts light only inthe specified direction, whereby light taking-out efficiency is not soenhanced. However, by changing the refractive index distribution to atwo-dimensional distribution, light is diffracted in all directions toenhance the light taking-out efficiency.

As noted above, the diffraction grating may be positioned at theinterface between any layers or in a medium (in a transparent substrateor a transparent electrode), but is preferably positioned adjacent tothe organic light emitting layer where the light is generated.

At the time, the cycle of the diffraction grating is preferably by afactor of about ½ to about 3 of the light wavelength in the medium.

It is preferable that the arrangement of detraction gratings istwo-dimensionally repeated to result in a square lattice, a triangularlattice or a honeycomb lattice.

<<Light Collecting Sheet>>

With regard to the organic EL element of the present invention, it ispossible, for example, to enhance luminance in a specified direction bycollecting light in a specified direction such as toward the front withrespect to the light emitting element surface by forming a micro-lensarray structure or by combining it with a so-called light-collectingsheet.

The micro-lens array is, for example, formed in such a manner thatquadrangular pyramids of a side length of 30 μl and an apex angle of 90degrees are two-dimensionally arranged on the light taking-out side of asubstrate. The side length is preferably 10-100 μm. When the length isless then the lower limit, diffraction effects occur to result incoloring, while when it is more than the upper limit, the undesirablethickness results.

It is possible to employ, as the light collecting sheet, ones which arecommercially employed, for example, as in LED backlights of liquidcrystal display devices. It is possible, for example, to employ, as suchsheets, luminance enhancing film (BEF), produced by Sumitomo 3M Ltd.Examples of the shape of the prism sheet may include ones in which Ashaped stripes of an apex angle of 90 degrees and a pitch of 50 μm areformed on a substrate and the others such as a shape in which the apexangle is rounded, a shape in which the pitch is randomly changed orother appropriate shapes.

Further, in order to control the light radiation angle from the lightemitting element, a light diffusing plate-film may be simultaneouslyemployed with a light collecting sheet. For example, it is possible toemploy the diffusion film (LIHGT-UP) produced by Kimoto Co., Ltd.

<<Preparation Method of Organic EL Elements>>

As one example of the preparation method of the organic EL element ofthe present invention, described will be a preparation method of theorganic EL element composed of an anode/positive hole injectinglayer/positive hole transporting layer/light emitting layer/electrontransporting layer/electron injecting layer/cathode.

Initially, a thin film of a thickness of at most 1 μm, but preferably10-200 nm, which is composed of desired electrode compounds such asanode compounds, is formed on an appropriate substrate, employing amethod such as a vapor deposition or sputtering method, whereby an anodeis prepared.

Subsequently, on the above film, formed is a thin organic compound layercomposed of a positive hole injecting layer, a positive holetransporting layer, a light emitting layer, an electron transportinglayer, and positive hole inhibition layer.

As noted above, methods to form each of these layers include a vapordeposition method, as well as wet processes (such as a spin coatingmethod, a casting method, an ink-jet method, or a printing method). Inthe present invention, in view of ease of formation of a homogenous filmand reduced formation of pin holes, preferred is film formationemploying methods such as a spin coating method, an ink-jet method, or aprinting method, but the ink-jet is particularly preferred.

In the present invention, during formation of a light emitting layer, itis preferable that a film is prepared via a coating method employing aliquid composition in which the organic metal complexes according to thepresent invention are dissolved or dispersed, and the coating method ispreferably the ink-jet method.

As liquid media in which the organic metal complexes according to thepresent invention are dissolved or dispersed, employed may, for example,be ketones such as methyl ethyl ketone or cyclohexanone; aliphatic acidesters such as ethyl acetate; halogenated hydrocarbons such asdichlorobenzene; and organic solvents such as DMF or DMSO. Further, itis possible to achieve dispersion via dispersing methods employingultrasonic waves, high shearing force dispersion, or media dispersion.

After forming these layers, in order to form a cathode, a thin layer ofat most 1 μm, composed of cathode compounds, is applied onto the abovelayers to result in a layer thickness in the range of 50-200 nm via avapor deposition or sputtering method, whereby a desired organic ELelement is prepared.

Further, by reversing the preparation order, it is possible to achievepreparation, in the order of a cathode, an electron injecting layer, anelectron transporting layer, a positive hole transporting layer, apositive hole injecting layer, and an anode. When direct electriccurrent voltage is applied to the multicolor display device prepared asabove, application of voltages of 2-40 V, employing the anode as + andthe cathode as −, makes it possible to observe light emission. Further,alternating current voltage may be applied, and the waveform of theapplied alternating electric current is not limited.

<<Application>>

It is possible to employ the organic EL element of the present inventionas various light emitting light sources. Examples of such light emittinglight sources include, but are not limited to, home illumination, carinterior illumination, backlights for watches and liquid crystals,advertising displays, signals, light sources for optical memory media,light sources for electrophotographic copiers, light sources for opticalcommunication processors, and light sources for optical sensors. Ofthese, it is possible to effectively employ the above EL element for useas a backlight of liquid crystal display devices and light sources forillumination.

If desired, the organic EL element of the present invention may besubjected during film production to patterning via a metal masking orink-jet printing method. When the above patterning is carried out, onlythe electrode may be subjected to patterning, the electrode and thelight emitting layer may be subjected to patterning, or all layers ofthe element may be subjected to the above patterning.

EXAMPLES

The present invention will now be described with reference to examples,however the present invention is not limited thereto.

Example 1 Preparation of Organic EL Elements 1-1 Through 13

After applying patterning to a substrate (NA45, produced by NH TechnoGlass Corp.) which was treated in such a way that ITO (indium tinoxide), as an anode, was applied onto a 100 mm×100 mm×1.1 mm glasssubstrate to form a 100 nm film, the transparent substrate provided withthe above transparent ITO electrode was subjected to ultrasonic cleaningemploying isopropyl alcohol, was dried in desiccated nitrogen gas, andwas subjected to UV ozone cleaning for 5 minutes. The resultingtransparent substrate was adhered onto the substrate holder of acommercial vacuum deposition apparatus. On the other hand, 200 mg ofα-NPD was placed in a molybdenum resistance heating boat, 200 mg of CBPas a host compound was placed in another molybdenum resistance heatingboat, 200 mg of basocuproin (BCP) was placed in further anothermolybdenum resistance heating boat, 100 mg of Ir-12 was placed in stillanother molybdenum resistance heating boat, and 200 mg of Alq₃ wasplaced in yet another molybdenum resistance heating boat. These boatswere then fitted onto the vacuum deposition apparatus. Subsequently,after lowering the pressure of a vacuum tank to 4×10⁻⁴ Pa, the aboveboat incorporating α-NPD was heated via electric current and vapordeposition was applied onto the transparent substrate at a depositionrate of 0.1 nm/second, whereby a 40 nm thick positive hole transportinglayer was produced.

Further, the above heating boats, respectively incorporating CBP andIr-12, were heated via electric current and co-deposition was appliedonto the above positive hole transporting layer at a deposition rate of0.2 nm/second and 0.012 nm/second, respectively, whereby a 40 nm thicklight emitting layer was produced. The substrate temperature duringdeposition was at room temperature.

Further, the above heating boat incorporating BCP was heated viaelectric current and deposition was applied onto the above lightemitting layer at a deposition rate of 0.1 nm/second, whereby a 40 nmthick positive hole inhibition layer was produced.

Still further, the above heating boat incorporating Alga was heated viaelectric current and deposition was applied onto the above positive holeinhibition layer layer at a deposition rate of 0.1 nm/second, whereby a40 nm thick electron transporting layer was further produced. Thesubstrate temperature during deposition was at room temperature.

Subsequently, 0.5 nm lithium fluoride and 110 nm aluminum each wasdeposited to form a cathode, whereby Organic EL Element 1-1 wasprepared.

Organic EL Elements 1-2 through 1-13 were prepared in the same manner asOrganic EL Element 1-1, except that CBP employed as the host compound ofthe light emitting layer was replace with each of the compounds listedin Table 1 as a host compound. Structures of the compounds employed inthe above are shown below.

(Evaluation of Organic EL Elements 1-1 Through 1-13)

Organic EL Elements prepared as above were evaluated. Table 1 shows theresults.

(Taking-Out Quantum Yield)

A constant electric current of 2.5 mA/cm² was applied to each of theprepared organic EL elements at 23° C. under an ambience of desiccatednitrogen gas and the taking-out quantum yield (in %) was determined.Spectroradiometric luminance meter CS-1000 (produced by Konica MinoltaSensing Inc.) was also employed for the above measurement.

Measured results of the taking-out quantum yield in Table 1 arerepresented by a relative value, with the measurement value of OrganicEL Element 1-1 being 100.

(Lifetime)

When driven at a constant electric current of 2.5 mA/cm², was the timedetermined at which luminance immediately after light emission (initialluminance) was lowered by one half. The resulting value was designatedas its half life time (τ0.5) and employed as an index of the lifetime.Spectroradiometric luminance meter CS-1000 (produced by Konica MinoltaSensing Inc.) was also employed for this measurement.

Measurement results of the lifetime in Table 1 are shown via relativevalues when Organic EL Element 1-1 is 100.

TABLE 1 Light Emitting Taking-Out Organic EL Layer Quantum ElementCompound Yield Lifetime Reference 1-1 CBP 100 100 Comparative Example1-2  (1) 134 152 Present Invention 1-3  (2) 138 131 Present Invention1-4  (4) 111 108 Present Invention 1-5  (5) 123 160 Present Invention1-6  (9) 111 118 Present Invention 1-7 (10) 114 103 Present Invention1-8 (11) 128 125 Present Invention 1-9 (15) 124 113 Present Invention1-10 (21) 132 150 Present Invention 1-11 (30) 135 160 Present Invention1-12 (32) 129 133 Present Invention 1-13 (36) 105 110 Present Invention

As can be seen from Table 1, organic EL elements of the presentinvention excelled in the taking-out quantum yield and realization oflonger lifetime.

Example 2 Preparation of Organic EL Full-Color Display Device

FIG. 1 is a schematic constitutional view of an organic EL full-colordisplay device. After applying patterning at a pitch of 100 μm to asubstrate (NA45, produced by NH Techno Glass Corp.) which was treated insuch a manner that an ITO transparent electrode (102) as an anode wasapplied onto glass substrate 101 to form a 100 nm film,non-photosensitive partition wall 103 (at a width of 20 μm and athickness of 2.0 μm) was formed between the ITO transparent electrodeson the above glass substrate via photolithography. The positive holeinjecting layer composition of the following formula was injected intothe space between the polyimide partition walls on the ITO electrode byemploying an ink-jet head (MJ800C, produced by Epson Corp.), followed bya drying process at 200° C. over 10 minutes, whereby positive holeinjecting layer 104 was prepared. Onto the resulting positive holeinjecting layer discharged was each of the following blue light emittinglayer composition, green light emitting layer composition, and red lightemitting layer composition, and each of the light emitting layers (105B,105G, and 105R) was formed. At the end, Al (106) as a cathode wassubjected to vacuum deposition so as to cover light emitting layer 105,whereby an organic EL element was prepared.

The prepared organic EL element results in each of the blue, green, orred light emission via applications of electric voltage to each of theelectrodes, whereby it was found that it was possible to employ them ina full-color display device.

(Positive Hole Injecting Layer Composition)

Aqueous PEDOT/PSS mixture 20 parts by weight dispersion (1.0% by weight)Water 65 parts by weight Ethoxyethanol 10 parts by weight Glycerin  5parts by weight PEDOT/PSS: poly(3,4-) ethylenedioxythiophene)-polystyrene sulfonate (produced by Bayer AG)

(Blue Light Emitting Layer Composition)

Ir Compound (1) 0.7 part by weight Ir-12 0.04 part by weightCyclohexylbenzene 50 parts by weight Isopropylbiphenyl 50 parts byweight

(Green Light Emitting Layer Composition)

Compound (1) 0.7 part by weight Ir-1 0.04 part by weightCyclohexylbenzene 50 parts by weight Isopropylbiphenyl 50 part by weight

(Red Light Emitting Layer Composition)

Compound (1) 0.7 part by weight Ir-9 0.04 part by weightCyclohexylbenzene 50 parts by weight Isopropylbiphenyl 50 part by weight

Further, it was found that organic EL elements which were preparedemploying Compounds (4), (19), (21), (28), (31), (32), and (40) insteadof Compound (1) were employable as a full-color display device.

Example 3 Preparation of Organic EL Element 3-1

After applying patterning to a substrate (NA45, produced by NH TechnoGlass Corp.) which was treated in such a manner that ITO (indium tinoxide), as an anode, was applied onto a 100 mm×100 mm×1.1 mm glasssubstrate to form a 100 nm film, the transparent substrate provided withthe above ITO transparent electrode was subjected to ultrasonic cleaningemploying isopropyl alcohol, dried in desiccated nitrogen gas, andsubjected to UV ozone cleaning over 5 minutes. The resulting substratewas mounted in a commercial spin coater and subjected to spin coating(at a film thickness of about 40 nm) under the conditions of 1,000 rpmand 30 seconds, employing a solution prepared by dissolving 60 mg of PVKin 10 ml of 1,2-dichloroethane, followed by drying under vacuum at 60°C. for one hour, whereby a positive hole transporting layer wasprepared.

Subsequently, spin coating (at a film thickness of about 40 nm) wascarried out at the conditions of 1,000 rpm and 30 seconds employing asolution prepared by dissolving 60 mg of Compound (1), 3.0 mg of Ir-9,and 3.0 mg of IOr-12 in 6 ml of toluene, followed by drying under vacuumat 60° C. for one hour, whereby a light emitting layer was prepared.

Further, spin coating (at a film thickness of about 10 nm) was carriedout at the conditions of 1,000 rpm and 30 seconds employing a solutionprepared by dissolving 20 mg of basocuproin (BCP) in 6 ml ofcyclohexane, followed by drying under vacuum at 60° C. for one hour,whereby a positive hole inhibition layer was prepared.

Subsequently, the resulting substrate was fixed onto the substrateholder of a vacuum deposition apparatus. On the other hand, 200 mg ofAlq₃ was placed in a molybdenum resistance heating boat, and fitted ontothe vacuum deposition apparatus. After lowering the pressure of a vacuumtank to 4×10⁻⁴ Pa, the above heating boat incorporating Alq₃ was heatedvia electric current and vapor deposition was applied onto the abovepositive hole inhibition layer at a deposition rate of 0.1 nm/second,whereby a 40 nm thick electron transporting layer was provided. Thetemperature of the substrate during deposition was at room temperature.

Subsequently, 0.5 nm lithium fluoride and 110 nm aluminum were depositedto form a cathode, whereby Organic EL Element 3-1 was prepared.

Electric current was applied to the resulting element, and almost whitelight was generated, whereby it was found that it was possible to employit as an illuminating device. It was also found that by replacingCompound (1) with each of Compounds (4), (19), (21), (28), (31), (32),and (40), white light was also emitted.

1. An organic electroluminescent element comprising at least an emissionlayer sandwiched between an anode and a cathode, wherein the emissionlayer comprises at least a compound represented by Formula (3)′,

wherein X represents O or S(R represents a hydrogen atom or asubstituent); A¹ and A² each represent a hydrogen atom or a substituentand at least one of A¹ and A² is a substituent having a nitrogen atom;L¹ and L² each represent a divalent linking group; n is an integer of 2or more; n3 and n4 each are 0 or
 1. 2. The organic electroluminescentelement of claim 1, wherein the compound represented by Formula (A) isfurther represented by Formula (1),

wherein X represents of O, S (R represents a hydrogen atom or asubstituent); n is an integer of 2 or more; A¹ and A² each represent ahydrogen atom or a substituent; and at least one of A¹ and A² each are asubstituent having a nitrogen atom.
 3. The organic electroluminescentelement of claim 2, wherein n is an integer of 2 to
 10. 4. The organicelectroluminescent element of claim 2, wherein n is an integer of 2 to4. 5-8. (canceled)
 9. The organic electroluminescent element of claim 1,wherein n is an integer of 2 or more to
 10. 10. The organicelectroluminescent element of claim 1, wherein n is an integer of 2 to4.
 11. (canceled)
 12. The organic electroluminescent element of claim 1,wherein the substituent having a nitrogen atom is a carbazolyl group.13. The organic electroluminescent element of claim 1, wherein thesubstituent having a nitrogen atom is a carbolinyl group.
 14. Theorganic electroluminescent element of claim 1, wherein the substituenthaving a nitrogen atom is a diarylamino group.
 15. The organicelectroluminescent element of any one of claims 1, wherein X is anoxygen atom.
 16. The organic electroluminescent element of claim 1,wherein the emission layer incorporates a phosphorescence-emitting metalcomplex.
 17. The organic electroluminescent element of claim 16, whereinthe phosphorescence-emitting metal complex is an Ir complex.
 18. Theorganic electroluminescent element of claim 1, generating emission ofwhite color.
 19. A display, comprising the organic electroluminescentelement described in f claim
 1. 20. A lighting device comprising theorganic electroluminescent element described in claim 1.